The advent of the use of magnetic resonance imaging ("MRI") in the practice of medicine gave a whole new dimension to non-invasive diagnostics. The accuracy of non-invasive diagnostics is directly related to the accuracy of the image produced by MRI. And the accuracy of the image produced by MRI is directly related to the field homogeneity produced in the imaging region of the magnet which is the heart of an MRI device. Inhomogeneities higher than 0.1ppm within the magnetic field produced by the magnet in an MRI device can provide distortion in the images produced. Such distortion may lead to an inaccurate diagnosis which, in the worst case, can lead to improper medical treatment.
The larger the volume of flux lines with high homogeneity produced by the magnet in an MRI device, the more useful the magnet is for MRI, as larger portions of the human body can be imaged with greater accuracy. Consequently, a need exists to provide magnets for use in MRI devices that provide imaging regions with high homogeneity which can accommodate larger and larger portions of the human body.
In addition to producing large imaging regions with high homogeneity, there is also a need associated with magnets used in MRI devices to provide improved access to the patient once the patient has been placed within the imaging region. Improved patient access facilitates interventional surgery or biopsies by medical personnel and the use of life-support equipment, if needed, while the patient is within the MRI device. Improved patient access also facilitates unrestricted access to both the head of the patient to administer anesthesia, or to the groin of the patient for the insertion of a catheter. It has also been found that improved patient access assists in reducing patient apprehension from the sensation of claustrophobia common among patients placed in tubular MRI magnets.
A need also exists to minimize the size and weight of magnets used in MRI devices. Such magnets must be of a size and weight that will allow for their installation in existing operating rooms without any extensive or undue modifications to existing construction.
There is finally a need in MRI devices that the magnet be of a size which facilitates installation in a variety of different positions or alternatively rotation or translation to a variety of different positions under hydraulic or mechanical control. Such translational or rotational capability will allow the magnet to accommodate the wide range of patient positions which accompany a broad spectrum of surgical procedures or imaging requirements.